Touch screen type

Touch screen type

Capacitive touch screen classification

The surface capacitive touch screen uses ITO (Indium Tin Oxide, a transparent conductive material) conductive film to sense the touch behavior of the screen surface through electric field induction. But the surface capacitive touch screen has some limitations, it can only recognize one finger or one touch.

The projected capacitive touch screen is a sensor that uses the electrodes of the touch screen to emit electrostatic field lines. There are two types of capacitors generally used in projected capacitive sensing technology: self-capacitance and interactive capacitor.

①Self-capacitive

Self-capacitance, also known as absolute capacitance, is one of the most widely used methods. Self-capacitance usually refers to the capacitance formed by the scan electrode and ground. On the glass surface, there are horizontal and vertical scanning electrodes made of ITO. These electrodes and the ground form the two poles of a capacitor. When touched by hand or touch pen, a capacitor is connected in parallel to the circuit, so that the overall capacitance on the scan line is changed. When scanning, the control IC scans the vertical and horizontal electrodes sequentially, and determines the coordinate position of the touch point according to the capacitance change before and after the scan. The notebook computer touch input board uses this method. The notebook computer input board uses an X*Y sensor electrode array to form a sensing grid. When the finger approaches the touch input board, a sensor is generated between the finger and the sensor electrode. A small amount of charge. Use specific algorithms to process signals from row and column sensors to determine the position of the finger.

② Interactive capacitive

Mutual capacitance is also called span capacitance, which forms capacitance at the intersection of the horizontal and vertical ITO electrodes on the glass surface. The scanning method of interactive capacitance is to scan the capacitance change at each intersection to determine the position of the touch point. When touched, it will affect the coupling of adjacent electrodes, thereby changing the capacitance at the intersection. The scanning method of interactive capacitance can detect the capacitance value of each intersection and the capacitance change after touch, so it needs scanning Compared with the self-capacitance scanning method, the time is longer, and X*Y electrodes need to be scanned. At present, the touch screens of smart phones/tablets, etc., all adopt interactive capacitive technology.